Resetting the poll times when the metric is cleared.

[vrdmr]

Description

Currently, the poll times are not reset, causing the stale first-poll time to show up in the reporting period. This change is to reset the poll periods.

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PR information

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This change is 

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (develop@2ffb7dc). Click here to learn what that means.
The diff coverage is 100%.

@@            Coverage Diff             @@
##             develop    #1583   +/-   ##
==========================================
  Coverage           ?   64.55%           
==========================================
  Files              ?       78           
  Lines              ?    11103           
  Branches           ?     1569           
==========================================
  Hits               ?     7168           
  Misses             ?     3595           
  Partials           ?      340

Impacted Files	Coverage Δ
azurelinuxagent/common/cgroupstelemetry.py	94.02% <100%> (ø)

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